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Federal boffins in the States say that the brave new future in which today's 'leccy-guzzling lights are replaced by efficient LEDs may not, in fact, usher in massive energy savings.

This is because, according to the scientists' research, people are likely to use much more lighting as soon as this becomes practical. The greater scope for cheap illumination offered by LEDs will simply mean that people have more lights and leave them on for longer.

"Presented with the availability of cheaper light, humans may use more of it, as has happened over recent centuries with remarkable consistency following other lighting innovations," says Jeff Tsao of the Sandia National Laboratory. "That is, rather than functioning as an instrument of decreased energy use, LEDs may be instead the next step in increasing human productivity and quality of life."

According to Tsao and his colleagues at Sandia, the fraction of gross domestic product spent on lighting has remained constant as candles were replaced by oil lamps, then again in the transition to the gaslight era, then yet again with the arrival of electric lighting. What changed with each of these innovations was that lighting became more and more common.

"Over the past three centuries, according to well-accepted studies from a range of sources, the world has spent about 0.72 percent of the world's per capita gross domestic product on artificial lighting," says Tsao. "This is so for England in 1700, in the underdeveloped world not on the grid and in the developed world using the most advanced lighting technologies. There may be little reason to expect a different future response from our species."

In particular, Tsao expects that an ageing population will resort to brighter lighting as its eyesight deteriorates.

"Improvements in light-efficient technologies may not be enough to affect energy shortages and climate change," says Tsao's fellow Sandia boffin Jerry Simmons. "Enlightened policy decisions may be necessary to partner with the technologies to have big impacts."